The invention disclosed herein pertains to a method and system for marking or applying information to insulated electrical conductors and other objects which are comprised of ink phobic materials such as fluorocarbon resins.
There are many occasions where it is necessary to mark insulated electrical conductors with information such as the wire size or the identity of the circuit in which the wire is involved. The insulation on wires and cables used in airplanes and space vehicles must be of the highest quality and must be marked to facilitate tracing and interconnecting.
The insulating materials which meet the requirements of airplanes, space vehicles and other critical applications to the highest degree are the fluorocarbons, sometimes called fluoroplastics. Polytetrafluoroethylene (PTFE), tetrafluoroethylene (TFE), fluorinated ethylenepropylene (FEP), perfluoroaloxy (PFA) and ethylene tetrafluoroethylene (ETFE), also known by the Du Pont Company trademark "TEFZEL" are typical of fluorocarbons or fluoroplastics which meet the indicated requirements. For the sake of brevity, fluorocarbon will be used herein as a generic word for PTFE and FEP of all grades which have the ink phobic properties of present concern. Fluorocarbons are characterized by low coefficients of friction, insolubility, extremely low adhesiveness, good temperature stability, good mechanical and electrical properties and non-flammability. Printing indicia or information on fluorocarbon wire insulation or other fluorocarbon objects having uneven surfaces has not been successful using conventional printing methods because the ink or dye by which the information is printed does not adhere to the fluorocarbon and is easily rubbed off. The avionics industry and military specifications require that identification information be applied on wire when it is specified and that the printing be durable and not removable by mechanical deformation or abrasion. As far as is known, no one has succeeded in applying durable printed information directly to fluorocarbon wire insulation or to fluorocarbon insulating cable sheathing which has an uneven surface such as is the case with sheathed cable comprised of twisted wires. Consequently, wire vendors have resorted to wrapping sleeves, made of ink compatible material, about fluorocarbon insulated wires and cables after printing whatever information is required on the sleeves. Surface tape labeling and tags are also used. Applying sleeves, tags or tape bearing printed information on fluorocarbon wires and cables raises the cost of the cable to the customer. These marking expedients, which are adapted because of the poor results obtained when printing on fluorocarbon surfaces before the present invention was made, increase the bulk and weight of wires and cables. Since there are miles of cables and wires on many aircraft and space vehicles and since the identifying media are applied frequently along the entire length of every wire or cable, the cumulative weight of the currently used marking media can become significant. The additional fuel consumed by an aircraft simply due to the weight added by discrete prior art cable and wire identifying media has significant value. Knowledgeable persons assert that it costs an airplane having an average duty cycle $800.00 to fly one pound of material over a period of one year.
Various schemes for treating cured fluorocarbon surfaces in a manner that would make them more susceptible to durable printing have been tried but none have been successful although durable printing has been achieved on fluorocarbon wire insulation surfaces immediately after extrusion or by use of a hot stamping method on round and regular surfaces.